Overlaying of plates

ABSTRACT

An apparatus for applying weld metal for the purpose of hard-facing of metal plates and a method of operation of the apparatus. A metal plate is moved through an apparatus in which there are weld heads including welding electrodes. The metal plate has a slight induced convexity in the region of the welding heads so that an accurate distance is maintained between the welding electrode and the surface of the metal plate. The convexity is formed by a wheel assembly under the plates and the wheel assembly may also include cooling means. The advantage of the flat plate system is that long lengths of plate may be hard-faced.

This invention relates to the overlaying of weld metal onto metal platesand in particular it relates to plates of the type in which the materialsuch as mild steel used in the production of various apparatus is facedwith a layer of weld metal deposited by welding means to provide a hardfacing or alloy cladding.

Overlaying of weld metal is already well known in the art and is usedfor instance in supplying tips to tools such as shears and the like usedin agriculture and it is also known to overlay plates by welding.Overlaying may also be used to face metal with another metal or alloy.

One method of overlaying plates is to form a plate into a cylinder andthen to fit this cylinder into a machine so as to rotate the cylinderbeneath an array of welding heads positioned to deposit a layer ofwelding material onto the plates progressively as it is rotated untilthe entire surface of the plates in its cylindrical form is covered,after which the plate is cut and straightened to produce the hard facedsheet of material. A problem in such an arrangement is first thatconsiderable work is entailed in forming the plates into a cylindricalform and then to straighten the plates into the form in which they willbe used during manufacture of products. Certain difficulties also existin control of the welding because of cylindrical form of the plate atthe time that the welding material was applied by the heads. It is alsoa practical restriction on the size of a plate which can be welded bysuch a method.

Another problem exists with weld overlaying is that in the sheetmaterial some portions of the sheet are heated more than others becausetwo welding heads pass over the same area and this gives an uneventhickness of weld metal overlay and perhaps some change to themetallurgical structure of the underlying metal.

It is an object of the present invention to provide an improved methodof manufacture and in order to carry out that method not subject to thedifficulties encountered heretofore and this is achieved according tothis invention by applying weld metal to form an overlay on the platewhile the plate is in planar form and hence without any need for thestep of cylindrical formation and subsequent flattening to planar form.

A further problem exists that when applying weld metal to a planar platethen some buckling can occur because of differences in temperature alongthe plate and hence this present invention includes means to preventproblems with distortion. Distortion causes a difference in distancebetween the metal and the welding head which causes arc instability andmay cause irregularities in weld metal deposition.

This present invention provides solutions to the above problems or atleast provides an alternative construction of machine.

In one form therefore the invention is said to reside in a weldoverlaying apparatus comprising drive means to draw a metal platesubstantially horizontally through the apparatus, and a plurality ofwelding heads arranged on a common oscillating carrier to oscillate foroscillating movement transverse to the direction of travel of the metalplate, characterized by an assembly positioned so as to be under themetal plate in use, wherein the assembly includes a slight upwardconvexity in the metal plate under the welding heads so as to accuratelyposition the metal plate with respect to the welding heads.

It will be seen that by providing the slight upward convexity the metalplate is held in tension so that buckling will be minimized and hencethe difference in distance between the surface of the metal plate andwelding electrodes will vary as little as possible and hence a more evenarc and a better lay down of weld metal will occur.

Preferably the assembly is a wheel assembly, and more preferably thewheel assembly is positioned under the welding head.

In one form of the invention the wheel assembly may include watercooling means whereby to cool the underside of the metal plate at thepoint of welding.

By cooling the metal plate at the point of welding minimum heat inputinto structure of the metal plate will occur and hence minimumdistortion will occur.

In a preferred embodiment the wheel assembly may include a plurality ofdiscs spaced apart on a central axis and the water cooling means maycomprise water spray heads between the discs and adapted to direct aspray of water towards the region the weld heads to strike the undersideof the metal plate when in use and hence cool the plate.

The weld overlaying apparatus according to this invention may furtherinclude flux and metal alloy powder addition means to apply a layer offlux and metal powder onto the surface of the metal sheet upstream ofthe weld head so that the flux and metal alloy powder can take part inthe weld application process.

The type of flux and metal alloy powder used will depend upon therequired hardness and/or metallurgical composition of the weld metaloverlay.

There may be further included a slag breaking wheel downstream from thewelding heads, the slag breaking wheel including a plurality of discs ona transverse axis and also including suction means to remove crackedslag.

The drive means may include drive rollers positioned above and below theline of travel of the metal plate and adapted to bear onto both upperand lower surfaces of the metal plate to securely hold the metal plateand move it forward as required. There may be drive means both upstreamand downstream from the weld head and these can be driven so that themetal plate is kept in tension in the region where it passes over thewheel assembly and underneath the weld heads.

The drive means may be adapted to move intermittently the metal plate atthe same time as the oscillation of the weld head reverses direction inits transverse travel. By this means the metal plate will be stationarywhile the plurality of weld heads transverse the plate but the platemoves forward when the weld heads reverse direction.

Each of the weld heads may include a continuously fed wire electrode andthe weld head may include means to drive the wire electrodes as they areconsumed in the welding process.

In a preferred embodiment of the weld overlaying apparatus according tothis invention adjacent weld heads may be transversely offset from eachother with respect to the direction of travel of the oscillatingcarrier. By such a transverse offset in the weld heads there will belimited localized heating caused by adjacent weld heads passing over ornear the same point on the metal please when each weld head reversesdirection. In one preferred embodiment the adjacent weld heads may beoffset by a distance which is equivalent to half the distance that theplate is intermittently moved forward during operation of the weldingapparatus.

In an alternative form the invention is said to reside in a method ofoverlaying weld metal onto a surface of a longitudinally moving metalplate for the purpose of hard facing or alloy cladding of the metalplate comprising the steps of laying down a layer of weld metal onto themetal surface by means of transversely reciprocating a set of weld headsacross the longitudinally moving metal surface characterized byimparting a slight convexity to the metal plate as it passes under theweld heads by means of a wheel assembly under the metal plate whereby toaccurately position the metal plate with respect to the weld heads.

A method according to this invention may further include the steps oflaying down a layer of flux and metal alloy powder onto the surface ofthe metal plate before the plate passes under the weld heads.

The longitudinally moving of the metal plate may be incrementally movedforward at the same time that the oscillatory movement of the weld headreverses direction.

The method of this invention may further include the step of cooling themetal plate from underneath the plate in the region of the weld heads bymeans of water spray jets associated with the wheel assembly.

It will be seen that by this invention there is provided an apparatus tolay a surface of weld metal onto a metal plate and because the metalplate is moved horizontally there is no restriction on the length of themetal plate.

This then generally describes the invention but to assist withunderstanding the invention reference will now be made to theaccompanying drawings which show a preferred embodiment of theinvention.

In the drawings:

FIG. 1 shows a side view in essentially schematic manner of a weld metaloverlaying apparatus according to the present invention,

FIG. 2 shows in schematic manner the arrangement of the oscillatorypaths of the weld heads according to a preferred embodiment of theinvention, and

FIG. 3 shows a cross sectional view of the apparatus shown in FIG. 1 inthe region of the weld heads again in schematic manner to show thearrangement of the wheel assembly and the weld heads.

Now looking more closely at the drawings it will be seen that the weldoverlaying apparatus of the present invention comprises upstream drivemeans 1 and downstream drive means 2 driven from a common drive shaft 3by means of chains 4 and 5. Upstream drive means 1 comprises lower drivewheel 6 and upper drive wheel 7 driven by a drive chain 8 with the metalplate 10 positioned between the upper and lower drive wheels 7 and 6.Idler wheel 11 and tensioning idler wheel 12 are provided to ensure thatthe chain 8 drives both wheels in their required direction.

The downstream drive assembly 2 comprises two lower drive wheels 15 and16 and a single upper drive wheel 17. Drive chain 20 passes over thedrive wheel 15, 16 and 17 and over idler wheels 21 and 22 and tensioningidler wheel 23 again to keep the chain in tension and ensure that allthe drive wheels are driven in the same direction. Again the metal plate10 passes over the lower drive wheels 15 and 16 and under the drivewheel 17.

The metal plate passes under a weld head assembly 30 and over a wheelassembly 31 between the upstream drive assembly 1 and the downstreamdrive assembly 2.

Other methods of driving the drive means may be provided such as shaft,gear or hydraulic drives.

With drive means both upstream and downstream from the welding stationthe metal plate can be kept in tension which will hold to reducedistortion during welding.

The wheel assembly 30 which can be seen more easily in FIG. 3 comprisesa central axis 35 supported on bearings 36 and a number of annular discs37 supported on the shaft 35. The discs 37 bear on the underside of themetal plate 10 and induce a slight convexity into the metal plate. Awater spray assembly 38 supplied from a water manifold 39 sprays waterbetween adjacent discs 37 to cool the underside of the metal plate 10.

Other embodiments of wheel assembly may be used to provide the slightconvexity. One embodiment may be a plurality of small wheels arranged inan arc to bear up under the steel plate.

The weld head assembly 30 comprises a reciprocating carrier 40 supportedby means (not shown) which are caused to reciprocate transversely to thedirection of travel of the metal plate by means of a motor 41 and crankassembly 42. In this embodiment four weld heads 43 are supported bybracket means 44 from the carrier 40.

Other numbers of weld heads depending upon the width of the plate to beoverlayed and drive means such as a linear motor may be used.

The welding heads in this embodiment are of the continuously wire fedtype and wire feed motor 46 drives wire feed drives 47 which feed wire48 through the weld heads so that respective welding tips 49 are adesired distance from the surface of the metal plate 10. Electricity issupplied to the weld head by means of cables 50.

The negative or ground electrode for the welding arrangement 75 may bepositioned on the apparatus to bear underneath the metal plate 10 to bein contact with the metal plate to ensure good electrical conductivityand the earth by means of cable 76.

Just upstream from the welding heads is the flux and metal alloy powderapplying means. This includes a hopper 60 which has a discharge end 62which is spaced apart from a flux and metal alloy powder applying roller51 so that a small amount of flux and metal powder exits through thehopper end 62 and is positioned on the roller 61 and as the roller 61 isdriven (by means not shown) the powder is deposited onto the metal plate10.

Immediately downstream from the weld heads 70 is the welding slagremoving station 70.

The welding slag removal station 70 includes a slag cracking wheel 71which comprises a plurality of annular discs fitted onto a central bossand which are run onto the weld surface of the metal arc of weldingwhich cause any slag on to the surface to crack. The cracks slag isdrawn by means of vacuum suction arrangement 72 before the slag crackingwheel and 73 after the slag cracking wheel.

As can be seen with particular reference to FIG. 2 the path of travel ofthe weld heads over the surface of the metal plate 10 is a series ofoscillatory or side to side movements.

Adjacent weld heads 80 and 81 are spaced apart in the direction oftravel of the metal plate by distance 82 which is approximately half thespacing between adjacent oscillations of the weld heads. It will be seenthat by this offset spacing the paths of adjacent welding heads do notcross and hence localized points of over-heating will not occur.

The method of operation of the weld metal overlaying apparatus accordingto this invention is as follows. A metal plate 10 is fed into theapparatus and the drive means 1 and 2 are driven in such a manner so asto keep the metal plate in tension where it passes over the wheelassembly 41. The metal plate also has a slightly induced convexitybetween the flux and metal powder adding roller 61 and the slag brakingroller 71. The convexity is carried by the wheel assembly 30 which bearson the under side of the metal plate between the rollers 61 and 71. Thisslight convexity ensures that a fixed distance is maintained between theupper surface of the metal plate 10 and the tip of the welding electrode49 whereby ensuring a constant arc size and hence constant depth of weldand consumption of the wire electrode 48.

It will be realized that with a crank assembly 42 driving the carrier 40in oscillating action the speed of the oscillating carrier will not beconstant across the entire width of travel as the change from rotatorymotion of the crank to oscillatory motion of the carrier will causeslowing down at the ends of the travel. Hence there may be providedelectronic control means (not shown) which detect the point at whichslowing down becomes significant and which speeds up the motor 41 at theend of each movement in each direction of the carrier so that it veryquickly transfers to the other direction of travel whereby preventinglocalized heating in the metal plate at the point of change of directionof the oscillating heads.

There may be provided computer control of the various parameters such aselectrode feed rate, oscillation frequency, plate speed, powderthickness and cooling rate, so that variation in one of the parameterscan be allowed for in the other parameters.

What is claimed is:
 1. A weld overlaying apparatus comprising drivemeans to draw a metal plate substantially horizontally through theapparatus, and a plurality of welding heads arranged on a commonoscillating carrier to oscillate for oscillating movement transverse tothe direction of travel of the metal plate, characterized by an assemblypositioned under the welding heads so as to be under the metal plate inuse, wherein the assembly induces a slight upward convexity in the metalplate under the welding heads so as to accurately position the metalplate with respect to the welding heads.
 2. A weld overlaying apparatusas in claim 1 wherein the assembly includes water cooling means wherebyto cool the underside of the metal plate at the point of welding.
 3. Aweld overlaying apparatus as in claim 2 wherein the assembly includes aplurality of discs spaced apart from each other on a central axis andthe periphery of these bearing onto the metal plate in use and the watercooling means comprising water spray heads between the discs and adaptedto spray water towards the weld heads.
 4. A weld overlaying apparatus asin claim 1 further including flux and metal alloy powder addition meansto apply a layer of flux and metal powder onto the surface of the metalplate to which the weld overlay is to be applied.
 5. A weld overlayingapparatus as in claim 1 further including a slag breaking wheeldownstream from the welding heads, the slag breaking wheel including aplurality of discs on a transverse axis and also including suction meansto remove cracked slag.
 6. A weld overlaying apparatus as in claim 1wherein the drive means comprises drive rollers positioned above andbelow the line of travel of the metal plate and adapted to bear onto themetal plate.
 7. A weld overlaying apparatus as in claim 6 includingdrive means both upstream and downstream from the weld heads whereby tohold the metal plate between the upstream and downstream drive means intension.
 8. A weld overlaying apparatus as in claim 1 wherein the drivemeans is adapted to move intermittently the metal plate at the same timeas the oscillation of the weld heads reverses direction.
 9. A weldoverlaying apparatus as in claim 1 wherein each of the weld headsincludes a continuously fed wire electrode and the weld heads includemeans to drive the wire electrodes.
 10. A weld overlaying apparatus asin claim 1 wherein adjacent weld heads are transversely offset from eachother with respect to direction of travel of the oscillating carrier.11. A weld overlaying apparatus as in claim 1 wherein the assembly is awheel assembly.
 12. A method of overlaying weld metal onto the surfaceof a longitudinally moving metal plate for the purpose of hard facing oralloy cladding of the metal plate comprising the steps of laying down alayer of weld metal onto the metal surface by means of transverselyreciprocating a set of weld heads across the longitudinally moving metalsurface, characterized by imparting a slight convexity to a metal plateas it passes under the weld heads by means of an assembly underneath themetal plate whereby to accurately position the metal plate in respect tothe weld heads.
 13. A method as in claim 12 further including the stepof cooling the metal plate from underneath the plate in the region ofthe weld heads by means of water spray jets associated with theassembly.
 14. A method as in claim 12 further including the steps oflaying down a layer of flux and metal alloy powder onto the surface ofthe metal plate before the plate passes under the weld heads.
 15. Amethod as in claim 12 further including the step of longitudinallymoving the metal plate incrementally forward at the time the oscillatorymovement of the weld heads reverses direction.
 16. A method as in claim12 wherein the assembly is a wheel assembly.